Whenever you hop on a straddleboard that has enchantments and another player breaks the board while you're still mounted you get 2 boards. The one you're currently stood on, and the one that dropped on the floor. Then proceed to disenchant the board using a grind stone, and rinse and repeat.

Came across this when me and a friend was messing about hitting each other.

Hope this gets patched, could be abused super easily.